This project will examine the intrinsic control of regional differentiation of fetal small intestine and the extrinsic factors which modulate it. Using our previously characterized fetal intestinal transplant model, investigations will be carried out in three interrelated areas: 1) The hypothesis that the differentiation of the intact fetal intestine in intrinsically controlled from the time that the intestine is morphologically identifiable will be fully tested. Current investigations have demonstrated that cytodifferentiation and morphogenesis are normal in intestine transplanted at 14 days of gestation. In further studies, transplant maturation will be assessed by detailed morphological analysis using light and electron microscopy. Since luminal factors are important in the processing of sucrase-isomaltase, their role in the maturation of the microvillus membrane enzymes will be assessed by the use of two-dimensional gel electrophoresis and by electrophoretic analysis of immunoprecipitated transplant lactase. 2) The developmental potential of endoderm alone from 14 and 15 day fetal intestine will be characterized using a successful method of separation of the layers and transplantation. The role of interaction between endoderm and mesoderm in the fetal intestine will be examined, utilizing promising long term in vitro methods which are now under intensive investigation. 3) The ability of the dissociated fetal intestine to reaggregate and produce organotypic development will be evaluated. Using the transplantation technique in combination with in vitro culture, we have demonstrated successful reaggregation and differentiation of trypsin-dissociated 18 day fetal intestine. Further experiments with this system will delineate the competent period during which the cells from the fetal intestine can reaggregate and differentiate. The long term in vitro model system will optimized and used to examine the role of protein and glycoprotein synthesis and of thyroid and adrenal hormones in reaggregation and differentiation of these cells. These investigations should provide significant insight into the relative roles in regional intestinal differentiation of intrinsic control, endoderm-mesoderm interaction, and extrinsic regulators.